Coating materials of this kind are known from, for example, WO 10/063332. The polyhydroxyl-group-containing compound (A) that is used in these coating materials is based on a hyperbranched, dendritic, hydroxy-functional polyester wherein at least one hydroxyl group is esterified with a C8 to C9 monocarboxylic acid. The result coatings exhibit high scratch resistance and weathering stability and also, at the same time, a good overall appearance, although even lower so-called short-wave values at increased film thicknesses of at least 40 μm are desirable. Also deserving of improvement in these coating materials are the sandability and polishability of the resultant coatings.
From WO 08/74491, WO 08/74490, WO 08/74489, WO 09/077181 and WO 10/149236, coating materials are known in which the compound (B) used, containing isocyanate groups and silane groups, is based on known isocyanates, preferably on the biuret dimers and isocyanurate trimers of diisocyanates, more particularly of hexamethylene diisocyanate. These coating material compositions have the advantage over conventional polyurethane coating materials of a significantly improved scratch resistance in combination with good weathering resistance. In need of improvement with these coating materials, besides the sandability and polishability of the resultant coatings, is the appearance. More particularly the overall appearance and the running tendency on vertical surfaces are to be improved.
Furthermore, EP-A-1 273 640 describes two-component coating materials comprising a polyol component and a crosslinker component, consisting of aliphatic and/or cycloaliphatic polyisocyanates or the polyisocyanates derived therefrom by polymerization, allophanate formation, biuret formation or urethane formation, where 0.1 to 95 mol % of the originally free isocyanate groups present have undergone reaction with bisalkoxy-silylamine. These coating materials can be used for producing clearcoats or topcoats in the automotive sector, and, following their complete curing, exhibit good scratch resistance in combination with good resistance to environment effects. This specification, however, contains no information on how the sandability and polishability and the appearance of the resulting coatings can be improved.
WO 07/033786, furthermore, discloses coating materials which as well as phosphonic diesters and diphosphonic diesters, as catalyst (A), comprise silane-group-containing mixtures (B), such as, for example, the mixture of the isocyanate-group-free reaction product (B1) of hexamethylene diisocyanate isocyanurate with N,N-bis(3-trimethoxysilylpropan-1-yl)amine and the isocyanate-group-free reaction product (B2) of isophorone diisocyanate isocyanurate with N-(3-trimethoxysilylpropan-1-yl)-N-n-butylamine, and also optionally, as further additives (C), polyacrylate resins or other binders and crosslinking agents. According to their hardness, the coatings produced from these coating materials again exhibit good scratch resistance combined with good resistance towards chemicals and environmental effects, but the weathering resistance is in need of improvement and the resultant coatings are decidedly brittle. Additionally, here again, there is a lack of details as to how the sandability and polishability and the appearance of the resultant coatings can be improved.
WO 2001/98393 describes two-component coating materials comprising a polyol as binder component and also, as crosslinker component, a mixture of a polyisocyanate (A) and a silane oligomer (B) which contains at least two isocyanate groups and additionally alkoxysilane groups, preferably bisalkoxysilane groups, and which is prepared by reaction of a polyisocyanate (PI) with alkoxysilylamines, preferably with bisalkoxysilylamines, more particularly with bis(3-propyltrimethoxy-silyl)amine. As polyisocyanate (A) and also as polyisocyanate (PI) for preparing component (B) it is preferred to use hexamethylene diisocyanate and isophorone diisocyanate and also their biurets and isocyanurates. These coating materials are used more particularly as primers and are therefore optimized for adhesion to metallic substrates, preferably to aluminum substrates. Details of how the most important properties for clearcoats, in particular the scratch resistance, on the one hand, and also, at the same time, the sandability and polishability and the appearance of the resultant coatings, on the other hand, may be improved are not present in this specification.
EP-B-1 527 144 describes 2-component clearcoat materials based on hydroxyl-containing polyacrylate resins, isocyanurate-group-containing hexamethylene diisocyanate as crosslinking agent, and a mixture of hydrophilic and hydrophobic nanoparticles based on silicon dioxide. These coating materials lead to highly glossy, scratch proof coatings that are free from surface defects. Still deserving of improvement, however, besides the scratch resistance and weathering stability, are, in particular, the optical properties, and especially the leveling values.
The as yet unpublished international patent application PCT/EP 2012/059611 and the international patent application PCT/EP2012/058355, not yet laid open, finally, describe coating materials of the aforementioned type that lead to coatings featuring enhanced polishability. This is achieved in particular through the use, as compound (B) containing isocyanate groups and silane groups, of a mixture of a compound (B1) having a cycloaliphatic polyisocyanate parent structure and a compound (B2) having an acyclic aliphatic polyisocyanate parent structure. The addition of rheological assistants based on fumed silica to the coating materials is not described in these applications.